This is another query about a possible electronics project. Having built a few circuits based on guidance from the BBS, I am emboldened!

I want to start work on the “perfect” rally computer. This could take 2-4 years to become functional and, like many things, may never really be done. Why? Well, traditional dedicated “A box” rally computers like Timewise and Alfa function very well but are closed systems – they use custom PROMs that aren't really accessible by owners and they rely on minute-by-minute management during rallies (enter new CAST/speed). At least one person has written a laptop-based rally computer, but, as we decided this past weekend, it suffers from the lack of a simple interface -- hitting the right function key when bouncing through a hairpin can be tough! (and the perfect LCD display does not exist yet). So, what I'd like to build is something that combines the good features from each – the ability to pre-enter complete rallies on a laptop then upload to rally computer combined with a simple, dedicated “A” box interface with big knobs, switches, and red LED counters. The attached graphic shows the general layout that I have in mind.

A few parts are not complicated. For instance, I built a VFD driver's display with serial input that was the one piece of our setup that worked without a hitch last weekend. Others, well, here's where my questions begin....

Driver Guide:

This is something I dreamed up – just LEDs that show yellow if on time, red if you need to slow down, green to speed up. It would not be powereed when ignition off, so power consumption not an issue. In my mind, it would receive 2 kinds of messages (from the main computer): Illumination/dim level (0-10) and LED pattern (which of 11 LEDs to illuminate at that moment, say in binary). As simple as can be – decisions about what 4 green LEDs mean can be made in the main computer/program and could be changed as desired. So, I guess my question is whether there is anyplace to start in the way of a pre-built board/circuit/PIC for this component.

Sensor pulse input:

This would have a 2-wire interface for up to 4 drop-to-ground pulse sensors which could range from 0.1 to 12 volts. The current pulse count for each sensor would be stored on the device until cleared with something deliberate like a shorted jumper. Each counter would read up to 9,999,999 this would be good for around 2000 to 5000 miles before reset depending on sensor mix. This small box would be connected to unswitched power – never powered off. So power consumption would be a critical issue. The counter storage method should be able to tolerate loss of power, though, in case of something like main battery fuse failure or maintenance that requires disconnect of ground/earth. The idea of this is to allow bad things like reboot to happen to main rally computer without messing up basic counters. Oh, and it needs to talk to the main computer. I indicated ethernet, but expect it could be serial – just a simply formatted counter message like: “0000322,0000822,0000000,0000833” All speed calculations would be performed (I think) on main box where odo factors are stored, but it could be useful to send factors to the sensor unit so that actual speeds could be returned along with counters.

So, ultra lower power consumption, separate persistent registers for each counter, ability to send (and maybe receive) via ethernet or serial. Is this a PIC? What kind of memory? Does it need a battery backup?

Main computer:

This box would support multiple display types simultaneously, red alphanumeric LEDs for counters, a VFD for a function menu, and maybe even a small 4x6 LCD panel for configuration/programming. It should support standard keyboard and pointer types. It would have Empeg-like functions (boot from flash) but use off-the-shelf parts. Power consumption should be as low as possible – perhaps use an inactivity timer to turn off LED/VFD display, but keep computer running overnight. It should be capable of running something like MySQL – what functions to load from what type of memory are TBD, but it would need to support some type of large-capacity storage for instructions, logging.

For all of this and for required serial, ethernet, VGA and keyboard/input requirements, it would look like I need some sort of SBC. I have looked at some of these, but can anyone recommend any one in particular? Say, some serial-centric ARM-based SBC with ethernet that would run directly from 12 volts? Do all of them use their own custom distro? Are there limitations WRT applications (like ability to run MySQL)? Some SBC outfits offer “developer kits”; is there one that is best/affordable?

This box could have 4-6 separate LED counters displaying. It seems unlikely that I could find a SBC with that many serial outputs and I wonder how to do this – can I just chain all of those LEDs together and address them with one long message?

Being much enamored of the Empeg menuing metaphor, I would expect to add a VFD menu system to control modes of operation. This would be controlled by knobs, toggle switches and maybe a 4-pole joytick. I know *nothing* about keyboard mapping on Linux machines, but is it feasible to take multiple dissimilar switch/button type and interface them through a single, custom keyboard map? Is there a place I can start to investigate this?

The Empeg's ability to store its state when powered off is something I would try to emulate – keeping configuration data like odo calibration factors, display settings etc. Most of the dedicated computers have no persistent settings thus driving the requirement to keep it powered up during breaks and long periods of inactivity.

One other general issue is the question of toolset and database interface. One of our group is a talented perl programmer and has written some nice rally calculation code (that could maybe fold into this) but I am skeptical of completing the required serial/keyboard sensor interfaces without resorting to C. In that respect, if there is any choice of PIC/SBC combinations that are best from a toolkit consistency standpoint, I'm all ears. Any other ideas or questions appreciated!!